"We want to understand where and how natural selection occurs," says Dr. Mark Shriver, associate professor of anthropology at Penn State. "However, most changes in genes are neutral and caused by the demographic history of the population."

Neutral demographic changes in populations occur because separated populations drift apart, decimated populations expand from smaller gene pools, and populations mix with each other.

Most individual mutations that occur in the genetic code are neutral or benign. These changes have no impact on the survival fitness of the individual and remain or disappear by chance. Some mutations destroy the ability of that part of the code to do its job, and the individual does not survive or reproduce relative to other members of the population. These individuals are generally selected out of the population because they are less fit. Other mutations accidentally provide a change that makes individuals more fit for their environment and gives them an advantage. These individuals are more fit and reproduce more, increasing the prevalence of that particular trait in the population.

"To identify genes that were naturally selected, it is important to know the demographic history of the populations being studied," says Shriver.

Researchers at Fred Hutchinson Cancer Research Center in Seattle created demographic models of possible population histories and applied them to genetic information from two populations one African-American and the other European-American sequenced at the University of Washington, Seattle. The four models represented populations that expanded exponentially, rapidly decreased to a small population size causing a bottleneck and then increased, where separated with only small amounts of in
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Contact: A'ndrea Elyse Messer
aem1@psu.edu
814-865-9481
Penn State
8-Sep-2004